Multi-mode subscriber units are designed to operate with multiple communication systems. Multi-mode subscriber units are further capable of operating in a large geographic area that is not limited to one communication system but is rather covered by multiple communication systems. A multi-mode subscriber unit operating within this larger geographic area may move from an area of coverage of one communication system to an area of coverage of another communication system. The multi-mode subscriber unit is required to switch between systems and perform the transition between communication systems in a timely manner incurring the smallest amount of transition time. In order for the multi-mode subscriber unit to be able to transition to a target communication system, the multi-mode subscriber unit must find a target cell location associated with the target communication system.
Finding the target cell location and connecting to the target communication system can consume time and increase current drain. A subscriber is likely to become frustrated with attempting to switch communication systems over an exceedingly long time period. The multi-mode subscriber unit may also be required to operate on two communication systems either simultaneously or in a time division multiplexed manner. On a current system, the subscriber may be able to initiate and receive interconnect telephone calls, while on another (target) system, the subscriber is required to initiate and receive dispatch calls. The subscriber therefore must locate candidate target cells on the target communication system. The subscriber must therefore switch its RF reception to these candidate target cells to monitor the target system and then revert back to its current system.
Therefore, the multi-mode subscriber unit generally keeps a list of candidate target cells in the supported communication systems. Candidate target cells are cells that have sufficient RF coverage to be utilized in the subscriber's area. Currently, the subscriber unit cycles through all cells in order to locate the target cell. Searching through all candidate target cells is an exceedingly time-consuming process. Accordingly, a more time efficient and streamlined technique for switching systems is needed.